PROJECT SUMMARY Current treatments for malignant gliomas, the most common being Glioblastoma Multiforme (GBM), include surgical resection, radiation, and chemotherapy but remain ineffective due to recurrence and therapeutic resistance. The inability to adequately treat these tumors may be due in part to a subset of tumor cells, cancer stem cells, that are resistant to many conventional therapies. Cancer stem cells within GBMs are localized to several areas, among them the perivascular compartment, which is a known cancer stem cell microenvironment or niche and has been shown to play a role in therapeutic resistance. Understanding how the cancer stem cells communicate with the perivascular niche to promote the cancer stem cell phenotype and promote therapeutic resistance is of immediate importance and has implications in the design of more effective glioma therapies. Recently, integrin alpha 6 has been identified in the perivascular niche of human GBMs and high expression correlates to cells with a cancer stem cell phenotype. Additionally, targeting of integrin alpha 6 resulted in compromised growth and tumor formation, demonstrating integrin alpha 6 could be a promising therapeutic target. The hypothesis of this proposal is that integrin alpha 6 is a unifying signal that promotes the cancer stem cell phenotype and will be evaluated by: 1) interrogating how integrin alpha 6 interacts with the perivascular microenvironment to maintain the cancer stem cell phenotype and 2) determining the role of integrin alpha 6 in promoting resistance to radiation and chemotherapy. The proposal also aims to develop an intravital imaging model of study the in vivo communication between cancer stem cells and the niche. Experimental studies will utilize human GBM specimens to evaluate extracellular matrix ligands present in the niche and utilize clinically relevant doses of radiation and chemotherapy to assess the impact of integrin alpha 6 targeting by RNA interference or blocking antibody administration. The cancer stem cell phenotype will be evaluated by self-renewal and tumor initiation assays. The long term objective of this proposal is to develop GBM therapies with increased therapeutic efficacy that target the cancer stem cells in combination with conventional therapies. These studies outlined in this proposal will uncover the critical role of cancer stem cell interaction with the niche via integrin 6 and evaluate potential therapies to GBM which disrupt niche related communication. Any findings and therapeutic developments may extend to other tumor types with a cancer stem cell component (i.e. colon, breast).